This invention relates to a novel configuration for a piston for a four-stroke cycle internal combustion engine.
Pistons having oval cross sections transverse to the axes of the cylinders in which they reciprocate along at least a part of their lengths are known. Conventionally, the major axis of the ellipse in the thrust and counterthrust face region of the skirt extends transverse to the axis of the wrist pin. There are, for example, the pistons illustrated and described in U.S. Pat. Nos.: 1,514,022; 2,262,132; 2,309,555; 2,513,814; 4,470,375; and, 4,648,309.
Published Japanese Patent Specification 1-104,951 discloses a piston having elliptical cross sections transverse to the piston and cylinder axes in the crown and ring band region. The major axes of these ellipses extend in the same direction as the axis of the wrist pin.
French Patent Specification 869,756 shows uniformly progressive ovality of a piston. The piston has cross-sectional ovality at the bottom of its skirt transverse to the piston pin axis, a progressive transition through a circular cross section in the plane of the piston pin axis transverse to the cylinder axis, and a continuing uniform transition to ovality in the opposite sense (that is, with the major axis of the oval parallel to the piston pin axis) at the crown of the piston. This runs counter to modern piston design, wherein the designer strives to optimize the competing considerations of heat transfer between the crown and cylinder wall on the one hand and clearance for reduced frictional loss on the other hand.
Applicant makes no representation by this discussion, nor should any such representation be inferred, that an exhaustive search of all relevant prior art has been conducted, or that no more pertinent prior art exists.
It is an object of the present invention to provide a piston design which reduces the so-called "dead volume" between the cylinder and the crown and top land region. Reduction of this dead volume enhances fuel efficiency and reduces emissions.
According to the invention, a piston for an internal combustion engine has a crown and top land region, an intermediate region including at least one additional land, and a skirt region. Cross sections through the crown and top land region transverse to the cylinder axis are ovals whose major axes are generally parallel to the axis of the piston pin. Cross sections through the intermediate region are either substantially circular or oval. Their longest dimensions are or equal to the length of the major axes of the ovals of the crown and top land region cross sections.
According to an illustrative embodiment of the invention, cross sections through the crown and top land region are uniform ovals.
Additionally, illustratively according to the invention, the longest dimensions of cross sections through the intermediate region are all substantially the same.
Further illustratively according to the invention, the longest dimensions of the cross sections through the intermediate region are less than the length of the minor axes of the ovals of the crown and top land region cross sections.
The piston further comprises a skirt region. The intermediate region is located between the crown and top land region and the skirt region. According to an illustrative embodiment, cross sections through the skirt region transverse to the cylinder axis are ovals whose major axes are generally perpendicular to the piston pin axes.
Illustratively, the lengths of the major axes of the cross sections through the skirt region increase uniformly from the junction of the skirt region with the intermediate region to about the middle of the length of the skirt region and then decrease from about the middle of the length of the skirt region to the remote end of the skirt region.
The invention may best be understood by referring to the following description and accompanying drawings which illustrate the invention.